Method of forming adhesive joint, structural subassembly, and joint construction

ABSTRACT

A method of forming an adhesive joint, a structural subassembly, and a joint construction. The method comprises telescopically assembling male and female tubular members having slightly different diameters to cooperatively define a narrow continuous open-end adhesive chamber between contiguous surfaces of the assembled members. Four (4) or more centering pins equally circumaxially spaced about the members are forcefully entered in the adhesive chambers to equalize spacing between the members throughout the chamber. A distributing device communicates with the adhesive chamber for the introduction of adhesive under pressure to the chamber, thus forming a secure joint. 
     In a fabrication method for a structural subassembly at least three (3) tubular structural members are loosely assembled with three (3) joint members each having at least two cups. Centering pins are forcefully introduced between contiguous surfaces of the members and cups and a distribution device encloses the open end of the adhesive chamber. Adhesive is then introduced between the contiguous surfaces of the members to form secure joints throughout. 
     A joint construction is produced in the practice of the method of the invention.

BACKGROUND OF THE INVENTION

Adhesive joints have been used in the past and while perhaps generally satisfactory have not been wholly satisfactory particularly in lightweight high strength structural applications. Two fundamental problems are encountered. One is the maintenance of precise relative positions of the members to be joined during the introduction and curing of the adhesive. At the present time this problem is solved by the use of extensive fixturing devices for securely holding the members during the application and curing of the adhesive. This procedure is not practical, however, for the high volume production of structural joints. A wind turbine tower with extensive structural steel lattice or truss work, for example, may involve hundreds and even thousands of joints.

The second problem resides in the provision of adhesive of uniform thickness throughout the area between the members to be joined. One current procedure involves the introduction of glass beads of a known diameter to the adhesive to provide uniform spacing but this of course reduces the amount of adhesive actively securing the joint and the beads may also introduce areas of stress concentration further reducing joint strength.

In view of the foregoing, it is the general object of the present invention to provide a method of forming an improved adhesive joint, a structural subassembly employing the method, and a joint construction all employing a self fixturing feature which overcomes the disadvantages of current practice and which is particularly well suited to high volume production as in wind turbine towers.

SUMMARY OF THE INVENTION

In fulfillment of the forgoing object and in accordance with the present invention, a method is provided which is particularly well suited to the fabrication of wind turbine towers of galvanized steel construction but which also has broad general application. The method contemplates the forming of an adhesive joint between telescopically assembled male and female members having cross sectional configurations which are similar but slightly different in size so as to cooperatively define a narrow continuous open-end adhesive chamber between contiguous surfaces of the assembled members. In the presently preferred form of the method of the invention, at least one and preferably four or more locating pins are inserted under pressure through the open end of the adhesive chamber into engagement with the contiguous surfaces of the two members and in spaced relationship about the members to equalize spacing between the same throughout the adhesive chamber. An adhesive distributing device provided with an inlet port encloses and communicates with the open end of the adhesive chamber. An adhesive is then injected through the inlet port preferably under pressure to fill the adhesive chamber uniformly throughout between the members to be joined. The adhesive is then cured to form a secure joint.

Preferably, a shoulder is provided on one of the members and preferably on the female member spaced from its open end and is engageable with the free end of the male member to act as a stop when the latter is inserted into the female member. A small insert of open cell foam positioned between the shoulder and the end of the male member allows air to pass but serves as a barrier to the adhesive and thus prevents the formation of air pockets or voids in the adhesive. In addition, this arrangement accommodates the use of a superior adhesive chamber filling process. Conventional gluing processes inject adhesive at a constant pressure and stop when a pre-selected volume has been injected. When porous open cell foam seals or other air permeable sealing arrangements are employed adhesive can be injected at a constant flow rate and terminated when a sharp rise in pressure is encountered. This is due to air at first passing through the seal and thereafter stopping abruptly when the seal is covered with adhesive throughout its surface area indicating a completely full adhesive chamber. This process insures complete filling of the adhesive chamber even though there may be substantial variation in volume of the chamber due to tolerances and other dimensional variations in manufactured parts.

The male member may be either solid or tubular and the female tubular or both members may be tubular, the term tubular referring to any generally hollow member which may be circular, oval, rectangular, triangular or of almost any cross sectional configuration. In the case of the wind turbine tower application of the invention, relatively thin walled tubing of circular and rectangular cross sections are employed in the form of galvanized structural steel.

As mentioned, the method of the invention is particularly well suited to the construction of subassemblies for wind turbine towers. Three or more elongated structural members of a subassembly may be loosely telescopically assembled to form loose joints with three or more connecting joint members each having at least one cup slightly different in diameter from that of the structural members. Centering means in the form of one or more and preferably four or five locating pins may then be inserted in each loose joint to firmly locate the structural and joint members relative to each other and to simultaneously provide adhesive chambers of uniform width at each joint. Employing distributing devices at each joint the adhesive chambers may then be filled with adhesive under pressure and cured to complete the subassembly.

The joint construction of the present invention is of course the product of the method of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat schematic sectional view of a joint construction of the present invention,

FIG. 2 is schematic sectional view taken generally as indicated at 2-2 in FIG. 1,

FIG. 3 is a view of a small insert used between the male member and an adjacent shoulder on the female member,

FIG. 4 is a view showing a locating pin employed as a self-fixturing means,

FIG. 5 is a view showing a pair of locating pins installed prior to the telescopic assembly of the male and female members,

FIG. 6 is a view of a female member with integral ribs employed as a centering means,

FIG. 7 is a fragmentary cross-sectional enlarged view showing a notch and chamfer in an open end of a female member, the locating pins thus being guided into an adjacent adhesive chamber,

FIG. 8 is a fragmentary cross-sectional enlarged view showing a short centering means formed integrally on the interior surface of a female member in spaced relationship with the mouth of the member, the centering means serving to center the free end of a male member entered in the female member,

FIG. 9 is a schematic perspective showing an adhesive distributing device mounted on an assembled male-female joint,

FIG. 10 is a sectional view through the adhesive distributing device of FIG. 9,

FIG. 11 is a schematic view showing a subassembly of a wind turbine tower structure employing the method and joint construction of the invention,

FIG. 12 is a fragmentary enlarged view showing a small annular insert at the inner end of the adhesive chamber around and in engagement with the outer surface of the male member and with and in engagement with the inner surface of the female member,

FIG. 13 is a fragmentary enlarged view showing an alternative embodiment of the invention with an adhesive port defined in a female member at an intermediate location and with annular seals at opposite ends of an adhesive chamber,

FIG. 14 is a fragmentary cross-sectional through an assembled joint comprising male and female members and an end cap mounted on the end of the male member and carrying an annular seal,

FIG. 15 is a fragmentary cross-sectional view similar to FIG. 14 but showing a slightly different end cap and seal arrangement,

FIG. 16 is a fragmentary cross-sectional view taken as indicated at 16, 16 in FIG. 15 and showing a plurality of sight holes spaced circumaxially about the end cap,

FIG. 17 is a fragmentary cross-sectional view similar to FIGS. 14 and 15 but showing an annular ring seal in a deep notch in an end cap,

FIG. 18 is a fragmentary cross-sectional view similar to FIG. 17 but showing a ring seal with a small flexible lip seal on the end cap.

FIG. 19 is a fragmentary cross-sectional view similar to FIGS. 17 and 18 but showing a flexible lip seal on the end cap without the ring seal of FIGS. 17 and 18, and

FIG. 20 is a fragmentary cross-sectional view similar to FIGS. 17 and 18 but showing a dovetail ring seal in a dovetail notch.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring particularly to FIGS. 1 and 2, an adhesive joint construction indicated generally at 10 includes telescopically assembled male and female members 12 and 14 which are similar in cross sectional configuration but which are different in size so as to cooperatively define a narrow continuous open-end adhesive chamber 16. The members 12 and 14 are both tubular with circular cross sections as shown but as mentioned above a wide variety of types of tubular and other male and female members may benefit from the teaching of the present invention. As is also mentioned above it is most important to maintain uniform thickness of the adhesive throughout the chamber 16 without pockets or voids in order to provide an efficient low cost joint of high structural integrity and lightweight.

In accordance with the method of the present invention, the male and female members are designed to provide adhesive chamber 16 of uniform width throughout when the members are telescopically assembled and small locating pins 18,18 are thereafter employed to fix the relative positions of the members and precisely establish the width of the adhesive chamber 16. At least one pin 18 is provided and as shown, four (4) equally circumaxially spaced pins 18,18 are inserted into the adhesive chamber 16 through its open end to positively fix the position of the members and the width of the chamber 16. The pins 18,18 are preferably inserted under pressure as with a pneumatic gun and thus serve a self-fixturing function for the joint.

As best illustrated in FIGS. 2 and 7, a series of small notches 19, 19 may be provided in equally circumaxial spaced relationship around the mouth of the female member 14. Each notch 19 has a shallow chamfer 21 at its inner end which is adapted to direct a locating pin 18 into an adhesive chamber in pressure engagement with the contiguous surfaces of the male and female members 12,14. Alternatively, locating pins such as 23,23 best shown in FIG. 5 may be employed as centering means and may be positioned in the mouth of the female member 14 prior to assembly of the same with the male member 12. A connecting loop 25 facilitates handling the pair of the locating pins 23,23.

In FIG. 6 a second alternative embodiment of centering means is shown with integral ribs 27, 27 formed in circumaxially spaced relationship on the interior surface of a rectangular tubular member 29 with two (2) ribs 27, 27 on one side of the member 29

Still further, short centering means 31 may comprise a single annular element or a number of individual ribs on the interior surface of the female member 14 spaced inwardly from the mouth of the member as best shown in FIG. 8. The annular element or ribs 31 serve as auxiliary centering means and engage and center the free end of a male member 12 as it reaches the end of its travel during assembly of the male and female members. The annular element or ribs 31 may be employed with any of the foregoing centering means.

With the adhesive chamber 16 properly sized and the members 12 and 14 secured in fixed positions by the pins 18,18, a distributing device 22 is positioned about open end 20 of the adhesive chamber 16, and as shown in FIGS. 9 and 10 encloses and has an inlet port 19 which communicates with the same for the introduction of an adhesive under pressure. Various adhesives may be employed but Loctite H8600 is presently preferred in an illustrative embodiment for joining the galvanized structural steel employed in wind turbine tower construction. A relatively low viscosity adhesive is of course preferred for rapid insertion in a high production environment. A uniform adhesive thickness less than fifty thousandths of an inch is found to provide the high strength low weight results desired with galvanized structural steel.

As mentioned above, the use of open cell foam seals accommodates an adhesive filling procedure based on pressure control and termination resulting in a completely filled adhesive chamber.

It should also be noted that the distributing device 22 may serve independently as a centering means avoiding the need for substantially all other centering means.

As mentioned, the prevention of voids in the adhesive is also important and a small open cell foam insert 24, FIGS. 3 and 8, captured and compressed between an annular shoulder 26 on the interior wall of the female member 14, and the inner end of the male member 12 prevents the entrapment of air and resulting pockets or voids. The insert is perforate to air and readily allows the same to pass but serves as an effective barrier to adhesive.

In FIG. 12 an annular seal 39 is shown about the inner end of a male member as an alternative embodiment. The seal 39 may be of open cell foam as above and also serves a preliminary centering function as well as a sealing function preventing the adhesive from escaping while allowing the air to pass.

Referring now to FIG. 11, it will be observed that three (3) elongated structural members 28,28 form a closed loop subassembly indicated generally at 30, which may be a part of a truss type wind turbine tower. Employing the teaching of the present method, the members 28,28 may be assembled as shown with their end portions entered loosely in cups 32,32, which form a part of connecting or joint members 34,34. Locating pins such as 18,18, not shown, may then be inserted circumaxially about the ends of the members 28,28 into adhesive chambers within the cups 32,32 in a self-fixturing operation. This is followed by positioning of adhesive distributing devices about the joints and the introduction of adhesive to fill the adhesive chambers thus completing the subassembly.

FIG. 13 illustrates an alternative embodiment of the invention with an adhesive port 40 formed for example by casting in a female member 42 at an intermediate location and communicating with an adhesive chamber 44. At opposite ends of the adhesive chamber 44 seals 46,46 are provided and may take the form of annular compressed open cell foam members as above.

FIG. 14 shows an assembled adhesive joint comprising male and female members 48 and 50 and end cap 52 mounted on the inner end of male member 48 and an annular seal 54 secured to the end cap. The inner annular surface 56 of the annular seal 54 is spaced inwardly from the external surface of the cap 52 and/or the surface 58 of the male member 48 and is adhesively attached to the cap 52. Thus, the cap 52 serves to protect the seal 54 on insertion of the insert and seal through the mouth of the female member 50 and axial sliding movement thereafter urging the male member to the assembled position shown in FIG. 14. This allows relative axial movement of the male and female members without loss of sealing efficiency. It should also be noted that the end cap 52 may serve as a centering means.

Referring to FIG. 15, a male member 48 a and female member 50 a are shown assembled with an end cap 52 a mounted on the male member 48 a and an annular seal 54 a mounted on the end cap. The end cap 52 a has an annular chamfer 60 at its free end portion which assists in aligning the cap during entry through the mouth of the female member 58.

The cap 52 a has a small annular portion adjacent the end of the male member 48 a which is externally exposed to the inner end of an adhesive chamber 64. Thus, when the cap is constructed of a transparent material, an annular indicator or sight opening is provided so as to visually ascertain whether the adhesive is distributed completely around the chamber 64.

In FIG. 17 an end cap 70 is provided with a somewhat deeper annular notch 72 than in prior configurations. An annular O-ring seal 74 is disposed in the notch and has only a small convex portion thereof exposed radially outwardly from the mouth of the notch. Engagement of the leading edge of the female member with the convex surface urges the annular O-ring seal radially inwardly into its notch to avoid excessive distortion of the same. The O-ring seal is preferably of compressible open cell foam.

FIG. 18 shows a design which may be identical to that of FIG. 17 except for the provision of a small flexible annular lip seal 76 which is formed on the end cap and which is adjacent the entrance surface of the projecting convex portion of the O-ring seal 74 a. As will be apparent, the lip seal 76 protects the ring seal 74 a during entrance of the male member through the mouth of the female member and prevents distortion of the seal. An air escape opening 78 may be provided or, alternatively, a series of circumaxially spaced small air escape slits may be provided in the lip seal 76.

FIG. 19 illustrates a configuration wherein a small flexible lip seal 76 a on the end cap serves as the sole adhesive sealing means and may also serve as a centering means. The lip seal 76 a is flexed radially inwardly during entry of the male member through the mouth of the female member and resides in compression in the assembled position of the members. A circumaxial series of small axial openings 78 a,78 a provide for the escape of air and a minimal amount of adhesive and may also serve as sight holes. Alternatively, the seal 76 a may be provided with a series of air escape slits as above.

Finally, it will be apparent for the foregoing that various cross sectional shapes may be employed for an O-ring seal in a notch such as the notch 72 a in FIG. 20. For example, a convex outer surface may be provided for an O-ring seal 74 b in FIG. 20 with the inner portion of the seal taking a rectangular configuration or alternatively, a dovetailed configuration may be utilized for secure retention of the inner portion of the seal as illustrated in FIG. 20.

End cap 52 b in FIG. 20 may be opaque with small sight openings provided at 66, 66 in a circumaxial array as illustrated in FIG. 16.

As will be apparent from the foregoing a relatively simple self-fixturing procedure has been devised as part of a highly efficient overall method providing a high strength low weight joint construction particularly well suited to high production joint formation as required in wind turbine tower fabrication at economic advantage. Substantial savings are realized in both material and labor costs as compared with conventional flange-bolt type joints as well as prior art adhesive joints. 

1. For use in constructing a wind turbine tower; a method of forming an adhesive joint comprising the steps of telescopically assembling male and female members having cross sectional configurations which are similar but slightly different in size so as to cooperatively define an open end adhesive chamber between contiguous surfaces of the members, providing centering means which engage the contiguous surfaces of the assembled members and substantially equalize spacing between the members throughout the adhesive chamber, providing an inlet port communicating with the adhesive chamber, injecting an adhesive through the inlet port to fill the adhesive chamber substantially uniformly throughout the area between the members to be joined, and curing the adhesive to form a secure joint.
 2. A method of forming a joint as set forth in claim 1 wherein the centering means takes the form of at least one locating pin positioned in the adhesive chamber and engaging the opposing contiguous surfaces of the adjacent male and female members.
 3. A method of forming a joint as set forth in claim 2 wherein at least one locating pin is positioned in the female member prior to the telescopic assembly of the male and female members.
 4. A method of forming a joint as set forth in claim 2 wherein the at least one centering and fixing pin is forcefully inserted into the adhesive chamber and into engagement with the contiguous surfaces of the male and female members subsequent to the telescopic assembly of the members whereby to both center the male member and firmly fix the male and female members relative to each other.
 5. A method of forming a joint as set forth in claim 1 wherein the centering means comprises at least one elongated integral longitudinally extending rib on one of the male and female members, which engages and centers the male member during telescopic assembly of the members.
 6. A method of forming a joint as set forth in claim 1 wherein at least one short centering means is provided on the surface of one of the male and female members spaced substantially inwardly from the mouth of the female member to engage and center the male member toward the end of the telescopic assembly of the members.
 7. A method of forming a joint as set forth in claim 1 wherein the female member is provided with a shoulder spaced from its open end and engageable with the free end of the male member to act as a stop when the latter in inserted into the female member.
 8. A method as set forth in claim 1 wherein the female member is effectively closed beyond the end of the assembled male member so as to prevent loss of adhesive and yet allow air to escape and thereby prevent voids in the adhesive.
 9. A method as set forth in claim 7 wherein an annular sealing insert is provided and is disposed between the shoulder and the inner end of the male member and allows air to pass but serves as a barrier to adhesive to prevent voids in the latter.
 10. A method as set forth in claim 1 wherein an annular sealing insert is provided and is disposed between the axially extending surfaces of the male and female members adjacent the inner end of the male member and allows air to pass and serves as a barrier to adhesive to prevent voids in the latter.
 11. A method as set forth in claim 10 wherein an annular end cap is provided for the inner end of the male member and mounts the annular seal with its inner surface spaced radially inwardly from the end of the radial end surface of the male member, the seal then being inserted into the mouth of the female member without distortion which might compromise sealing efficiency.
 12. A method as set forth in claim 11 wherein the end cap is provided with an annular chamfer to direct the same into the mouth of the female member.
 13. A method as set forth in claim 11 wherein the end cap is of a clear transparent plastic and serves as a visible indicator of uniform adhesive distribution about the radial end portion of the male member.
 14. A method as set forth in claim 11 wherein the small indicator openings are provided in the end cap for determining complete filling of the inner end portion of the adhesive chamber.
 15. A method as set forth in claim 11 wherein a deep annular notch is provided in the annular end cap and wherein a ring seal is provided in the notch with an outwardly projecting substantially convex surface in cross-section.
 16. A method as set forth in claim 15 wherein the end cap is provided with an inclined annular lip seal extending outwardly between radial and axial planes adjacent and toward the convex surface of the ring seal.
 17. A method as set forth in claim 1 wherein a flexible inclined annular lip seal is provided on the end cap and engages and is flexed radially inwardly during assembly of the male and female members, whereby to reside in sealing compression in the assembled state of the members.
 18. A method as set forth in claim 1 wherein the male member is solid.
 19. A method as forth in claim 1 wherein both the male and female members are tubular.
 20. A method as set forth in claim 19 wherein both the male and female members are thin-walled cylindrical tubular members,
 21. A method as set forth in claim 4 wherein at least three locating pins are provided in substantially equally spaced relationship around the members.
 22. A method as set forth in claim 21 wherein at least three (3) equally-circumaxially spaced entry notches are provided around the mouth of the female member each with a gradual chamfer for directing a locating pin into the adhesive chamber and into engagement with the male and female members.
 23. A method as set forth in claim 20 wherein the members are thin-walled cylindrical tubular members of galvanized structural steel.
 24. A method as set forth in claim 1 wherein an adhesive distributing device is positioned about the free end of the female member and has an inlet port communicating with the adhesive chamber.
 25. A method as set forth in claim 1 wherein an adhesive inlet port is provided in the female member intermediate its ends and wherein seals are provided at opposite ends of the adhesive chamber.
 26. A method as set forth in claim 1 wherein an annular seal is provided adjacent the inner end of the male member that allows air to pass but serves as a barrier to adhesive, and wherein adhesive is introduced to the adhesive chamber at substantially constant volumetric flow rate with injection being terminated when a pressure rise indicates adhesive covering the face of the seal and a completely full adhesive chamber.
 27. A method for fabricating a structural assembly for use in a wind turbine tower comprising the steps of providing at least three elongated tubular structural members arranged in spaced relationship with at least three associated joint members each having at least one short connecting member differing in diameter from the tubular structural members, the structural members and short connecting members thus being adapted for male-female telescopic assembly each having an annular open end adhesive chamber therebetween, positioning the structural assembly with the members and short connecting members in loose male-female telescopic relationship, providing centering means in each adhesive chamber to locate the structural members and short connecting members in substantially uniformly spaced relationship with resulting adhesive chambers of substantially uniform width therebetween, providing an inlet port communicating with each adhesive chamber injecting an adhesive into said inlet port whereby to fill said adhesive chamber uniformly throughout the area between the members to be joined, proceeding to second, third and all remaining joints, and repeating the adhesive injection procedure and curing the adhesive in all adhesive chambers to form secure joints throughout.
 28. A method for fabricating a structural assembly as set forth in claim 27 wherein said centering means comprises at least one locating pin forcefully inserted into each adhesive chamber to engage contiguous surfaces of the male and female members.
 29. A method for fabricating a structural assembly as set forth in claim 28 wherein at least one short centering means is provided on at least one of said male and female members spaced substantially from the mouth of the female member to engage and center the male member toward the end of the telescopic assembly of the members.
 30. A method for fabricating a structural assembly as set forth in claim 27 wherein each female member has a shoulder spaced from its open end engageable with the end of the male member and acting as a stop when the latter is inserted into the female member.
 31. A method as set forth in claim 27 wherein each female member is effectively closed beyond the end of the assembled male member.
 32. A method as set forth in claim 30 wherein an insert is positioned between the shoulder and the inner end of each male member and allows air to pass but serves as a barrier to adhesive loss.
 33. A method as set forth in claim 31 wherein an additional seal is provided adjacent the free end of the female member.
 34. A method as set forth in claim 27 wherein both the male and female members are thin-walled tubular members constructed of galvanized structural steel.
 35. A method as set forth in claim 31 wherein at least three (3) locating pins are provided and are equally spaced around the cylindrical tubular members.
 36. A method as set forth in claim 27 wherein said structural members are arranged in angularly displaced closed loop relationship with each other.
 37. A method as set forth in claim 27 wherein a fixture is provided and wherein said structural members and short connecting means are initially positioned in loose interconnection and in subassembly relationship with the aid of the fixture.
 38. A method as set forth in claim 27 wherein an annular end cap is provided for the inner end of the male member and adhesively mounts an annular seal with its inner surface spaced radially inwardly from the axial surface of the male member, the seal then being inserted into the mouth of the female member without rolling up and other distortion.
 39. An adhesive joint as set forth in claim 38 wherein an adhesive distributing device is positioned about the free end of the female member and has an inlet port communicating with the adhesive chamber.
 40. For use in a wind turbine tower; an adhesive joint between telescopically related male and female members having cross sectional configurations which are similar but slightly different in size so as to cooperatively define a narrow open end adhesive chamber between contiguous surfaces of the assembled members, at least one centering means positioned in the adhesive chamber and engaging the contiguous surfaces of the two members and substantially equalizing the space between the members throughout the chamber, said adhesive chamber being filled with adhesive uniformly throughout the area between the members to be joined.
 41. An adhesive joint as set forth in claim 40 wherein an adhesive distributing device is positioned about the free end of the female member and adhesive is introduced through an inlet port communicating with the adhesive chamber.
 42. An adhesive joint as set forth in claim 40 wherein the centering means takes the form of at least one locating pin in the adhesive chamber engaging the contiguous surfaces of the male and female members in a press fit.
 43. An adhesive joint as set forth in claim 40 wherein at least one integral rib comprises the centering means and projects from the surface of one of the male and female members to engage the contiguous surface of the male member.
 44. An adhesive joint as set forth in claim 40 wherein a centering means includes at least one short rib on the interior surface of one of said male and female members spaced substantially from the mouth of the member to engage and center the male member toward the end of a telescopic assembly of the members.
 45. An adhesive joint as set forth in claim 40 wherein one of the male and female members has a shoulder spaced from its end engageable with the end of the opposite member and acting as a stop when the male member is in inserted into the female member.
 46. An adhesive joint as set forth in claim 42 wherein an annular sealing insert is disposed between the shoulder and the inner end of the male member and allows air to pass but prevents adhesive loss.
 47. An adhesive joint as set forth in claim 40 wherein an annular sealing insert is disposed about the male member and in engagement with the axially extending surface of the female member adjacent the end of the male member and allows air to pass but prevents adhesive loss.
 48. An adhesive joint as set forth in claim 40 wherein both male and female are thin thin-walled tubular members of galvanized structural steel.
 49. A method as set forth in claim 40 wherein an annular end cap is provided for the inner end of the male member and adhesively mounts an annular seal with its inner surface spaced radially inwardly from the end of the radial end surface of the male member, the seal thus being inserted into the mouth of the female member without rolling up and other distortion.
 50. A method as set forth in claim 49 wherein a deep annular notch is provided in the annular end cap and wherein a ring seal is disposed in the notch with an outwardly projecting substantially convex surface.
 51. A method as set forth in claim 49 wherein the end cap is provided with an inclined annular lip seal adjacent the convex surface of the ring seal.
 52. A method as set forth in claim 40 wherein a flexible inclined annular lip seal is provided on an end cap for the male member and engages and is flexed radially inwardly during assembly of the male and female members whereby to reside in sealing compression in the assembled state of the members. 